Depending on the material and the workpiece to be treated, a wide variety of different types of radiation can be used. For example, radiation from the electromagnetic spectra can be used. The wavelength can differ in a wide range and can be, as an example, chosen from the radiomagnetic spectra, the infrared spectra, the visible spectra, the ultraviolet spectra up to the x-ray spectra and even higher. Another possible form of irradiating workpieces is in the form of particle irradiation, in particular in the form of accelerated particle beams. The particles themselves can be chosen from a wide variety as well. As an example, leptons like electrons or positrons can be used. Also hadronic particles can be used like protons, light ions (for example protons, ionized helium atoms) as well as heavy ions (for example carbon ions, oxygen ions and neon ions). Other possible hadronic particles are pions, mesons and so on. The possible energies for such particles can vary from low energies like several kilo electron volts up to speeds close to the speed of light with energies in the range of several hundred mega electron volts, or even in the giga electron volts range.
Whereas a possible application for irradiating material lies in applications, where the workpiece to be treated has to be irradiated in a uniform way, for example when a material has to be modified by irradiation other applications exist, where the irradiation has to be applied with a certain pattern. One technological field, where such patterned irradiation is necessary is the production of microprocessors or nanomechanics. Here, certain parts of the surface of the workpiece to be treated have to be irradiated, while other parts should not be irradiated at all. This is done by using patterned masks, which are irradiated by a homogeneous radiation source. Another possible way of applying such structured radiation is to use a pencil-like beam and to move the spot of said beam across the surface of the workpiece in a particular pattern.
Nowadays, not only two-dimensional treatment of workpieces is performed, but also three-dimensional irradiation of workpieces. This way, it is even possible to deposit a certain radiation dose inside the workpiece without opening said workpiece. Hence, a treatment of a three-dimensional section within a workpiece is possible.
Another complexity arises, when a moving workpiece or a workpiece with moving parts has to be treated. Here, the application of an irradiation has to be performed in a way that the movements of the body are considered when irradiating said workpiece. This is frequently referred to as a four-dimensional application of radiation (where time is considered to be the fourth dimension).
A movement of the workpiece cannot only occur with respect to an external reference frame, but can also occur by relative movements of parts of said workpiece against other parts of said workpiece. Therefore, rotational deformations, longitudinal deformations and quenching of material have to be considered.
Of course, not only inorganic material can be treated by applying radiation, in particular particle beams. It is also possible to treat organic matter and even living tissue of animals and human beings. One possible application for three-dimensional or four-dimensional application of radiation is the treatment of cancer. Here, a certain area of the human body in particular the tissue, which is infected by tumour cells, has to be treated with a certain irradiation dose, so that the cells within this volume are destroyed or at least damaged. Of course, the surrounding healthy tissue should be protected by applying very little radiation, if at all.
If particular, for the treatment of tumours, particle beams, in particular hadronic particle beams (even more preferably heavy ion particle beams) have proven to be very useful. This is because particle beams show a pronounced so-called Bragg-peak. That is, the energy of a particle, moving through tissue, is not deposited equally over the particle's path. Instead, the majority of the particle's energy is transferred in the very last part of the path, before the respective particle gets stuck.
An problem when treating three-dimensional structures, in particular human beings with individual characteristics, is that first the areas, where the radiation has to be deposited, has to determined. This should be done by methods, which do not need to open the workpiece, in particular a patient having the tumor, to be treated (so-called non-invasive methods), because otherwise the advantage of three-dimensionally structured radiation would be lost.
For performing this task, usually three-dimensional imaging techniques (or even four-dimensional imaging techniques, taking into account movements) are used. Examples of such techniques are ultrasonic imaging techniques or computer tomography methods. However, these methods show disadvantages as well. With computer tomography, a major disadvantage is that an additional radiation dose is applied to the body. In particular, when a four-dimensional image has to be taken and/or a continuous imaging during the treatment itself is needed, this additional radiation dose can be substantial. Therefore, there is a tendency to reduce the additional radiation level as far as possible.
The disadvantage of applying an additional dose can be avoided by using ultrasonic imaging techniques. However, the image quality is sometimes far from perfect. Another major disadvantage of ultrasonic imaging techniques is that they cannot be used during the treatment with hadronic particles at all.
A possible way out is to use the above mentioned imaging techniques (or even other methods) and to link the thus determined movements to so-called movement substitutes. This can be achieved by correlating the three-dimensional pictures, gained by computer tomography or ultrasonic imaging techniques to a substituting signal, like the picture of a standard video camera or a signal from a length measuring strap, which is attached to a patient's chest or the like. Although such substitutes work relatively well in practice, the maximum resolution achievable is limited.
Another disadvantage, not yet mentioned is that the density of the tissue, as seen by the particles (and hence the penetration length of the particles) can be substantially different from the density of tissue, as seen by leptonic particles, phonons (ultra sonic imaging techniques) or photons (x-ray imaging techniques). Experiments have shown that this gives rise to sometimes substantial errors.
Hence, there is still a necessity for a method on how to determine distinct features within a workpiece or a body and/or the movement of different regions of the workpiece or the body (in particular the body of a patient) during the treatment of said workpiece or body.